This invention relates to a drum brake device, in which a brake shoe opens mechanically. More specifically, this invention relates to an improvement in a preventive means for an inner cable coming off from a brake lever.
A drum brake device publicly known is a device in which the base end of a brake lever is pivotably mounted on the brake shoe. An inner cable which is an element of a parking brake cable is inserted through a U-shaped folded pocket formed at the tip of the brake lever, and a cable end fixed on the tip of the inner cable hooked on the U-shaped folded pocket of the brake lever at a non-pulling direction side. This is a brake device in which brake shoes are mechanically opened by pulling the inner cable from the outside of the drum brake.
Such a publicly known drum brake device has a possibility of the inner cable coming off from the U-shaped folded pocket while transporting or handling the drum brake device. As a preventive means for the inner cable coming off from the brake lever, in the Japanese Utility Model Gazette Number 2520404, one portion of brake shoe rim is notched and raised toward the inside of the brake shoe to form a projection, and the lengthwise travel of the cable end along the brake shoe rim is restricted to a certain range.
The above-explained method of preventing the inner cable from coming off has several points which may be improved. For example, if a projection restricting the lengthwise travel of the cable end is formed only on one brake shoe, relative to a pair of right and left brake shoes, the right and left brake shoes become dissymmetrical, thereby creating a possibility of misassembly as well as a problem of intricate parts maintenance.
In addition, if the projections restricting the lengthwise travel of the cable end are formed by modifying a section the shoe rim, such as by punching and bending two portions of the shoe rim to form cable-stopping projections on both sides of the shoe web in order to commonly design a pair of right and left brake shoes, the moment of inertia of area is reduced corresponding to the area of the modified section, thereby reducing the rigidity of the shoe rim.
Generally, a plurality of welding projections are provided at the center of the width direction of the shoe rim in order to be integrated with the shoe web. A plurality of beads may also be formed at some portions (normally three portions) of each side end of the width direction of the shoe rim so as to reduce the sliding resistance force for sliding on some ledge surfaces formed on the back plate when either opening or closing the brake shoes. A bead may be formed in an almost rectangle by bending the shoe rim in a right angle or a semicircle by drawing.
In addition, for restricting the lengthwise travel of the cable end, the shoe rim may be modified to form the cable-stopping projection between the welding projection and the bead, which makes it difficult to conduct the R-bending of the shoe rim corresponding to the periphery of shoe web by the rollering process. This forces manufacturers to conduct the R-bending by press with low efficiency. Especially, efficiency in forming the brake shoe is reduced as the shoe rim width becomes narrower.
A punched and bent cable-stopping (half blanking) projection may be added in a shoe rim pressing die, and an additional step of pressing for the projection may be included. These create needs for an improvement to reduce the cost.
This invention was made to mainly improve the above-mentioned points, and to that end, it is an object of this invention to provide a mechanical type drum brake device which prevents a cable end from coming off from a brake lever without requiring an additional part as well as making an improvement in a brake shoe and a brake lever. It is another object of this invention to provide a mechanical type drum brake device which is more economical.
In one aspect, an apparatus in accordance with the invention includes a brake shoe having a shoe rim, an approximately J-shaped brake lever rotatably pivotable with respect to said brake shoe and having a U-shaped folded pocket formed at a free end of said brake lever, a lever return spring stretched between said brake shoe and said brake lever, an inner cable of a parking brake cable inserted in said U-shaped folded pocket, and a cable end fixed on said inner cable hooked at a non-pulling side of said U-shaped folded pocket, said brake lever being rotatably pivoted by pulling said inner cable, thereby opening said brake shoe, wherein a movement of said cable end in the direction that said cable end travels lengthwise toward and along said shoe rim is restricted by said lever return spring. Alternately, the lever return spring may be a torsion spring, a tension coil spring, or some other type of spring.